Conventionally, the portable telephone has been used mainly for the speech communication function. Therefore, the communication network of portable telephone is formed on the basis of a circuit switching network. Even during data communication, the portable telephone network must use the circuit switching.
As the Internet spreads, the communication network of portable telephone is currently evolving so as to incorporate the data communication function and multimedia function. Recently, data communication of portable telephone is switching over to communication networks of packet communication utilizing packet switching, which is called i mode in Japan and General Packet Radio Service (hereafter abbreviated to GPRS) abroad.
In data communication using portable telephone, interleaving is carried out in channel coding processing for the purpose of reducing burst errors. FIG. 1 is a block diagram showing a configuration of a processing section of the transmission side, which conducts channel coding processing. The processing section includes an error correction coding section 101, an error correction coding section 102, a punctured coding processing section 103, and an interleaving section 105. The error correction coding section 101 conducts block coding on packet data blocks, and out puts a result thereof. The error correction coding section 102 conducts convolutional coding on data output from the error correction coding section 101, and outputs resultant data. The punctured coding processing section 103 conducts punctured coding (thinning) on data output from the error correction coding section 102, and outputs resultant data. The interleaving section 105 conducts interleaving on data output from the punctured coding processing section 103, and outputs resultant data.
Once a communication channel is established in data communication utilizing circuit switching, the circuit is maintained in the connected state until the communication channel is disconnected. In data communication utilizing circuit switching, therefore, continuity of burst signals is basically assured. In this case, the burst length of interleaving is determined by considering first an effect of reduction of burst errors, secondly divisors of the total number of bits of data signals to be interleaved, thirdly a communication buffer capacity required for interleaving, fourthly a transmission delay time permitted between transmission and reception, fifthly a kind of communication data such as voice data and video data, and sixthly radio wave propagation characteristics such as fading. For example, in full rates 4.8 kb/s (kilobits per second), 9.6 kb/s, and 14.4 kb/s in data communication of potable telephone of GSM scheme, the burst length of interleaving is 19.
On the other hand, in packet communication utilizing a packet switch, communication channels are shared with other communication in time division, and consequently the continuity of burst signals is not necessarily assured. In such packet communication, each radio block having a predetermined number of (4 in the GPRS) burst signals is handled as a basic unit. Interleaving is carried out by using a predetermined number of burst signals.
FIG. 2 is a block diagram showing a data configuration of a radio block in GSM portable telephone. As shown in FIG. 2, the data includes some radio blocks. Radio blocks 1 to 3 are shown in FIG. 2. Each of the radio blocks 1 to 3 includes four consecutive burst signals. Each burst signal includes two data signals, two flag signals, and an synchronizing signal.
The subject of interleaving in the radio blocks shown in FIG. 2 is only the data signals. The flag signals and the synchronizing signals do not become the subject of interleaving. If it is assumed that the burst length of data signal interleaving is 4, data signals (1) to (8) are thrown into one and then interleaved.
In the GSM potable telephone, the data signals interleaved as described above are further rearranged in respective burst signals in accordance with a predetermined rule. Thus, two-dimensional interleaving is conducted.
FIG. 3 is a diagram showing a method of interleaving in the case where the burst length of interleaving is 4 as described above. It is now assumed that the total number of bits of data signals included in each radio block is 448 and the number of bits of data signals included in each burst signal of the radio block 2 is 112. Denoting a data sequence of data signals included in each radio block by Y (0 to 447), the data signals are written into a matrix-formed memory in its column direction in order, beginning with 0. If data of the radio block are written into the memory, the data in the memory are read out in its row direction. In this way, interleaving is carried out. Therefore, a data sequence assigned to nth burst signal after the interleaving can be represented as Y=4m+(n−1) (where m=0 to 111, and n=1 to 4). In packet communication, the above-described continuity of burst signals is not assured. Therefore, it is necessary that the burst length (4) of interleaving in packet communication coincides with the number (4) of burst signals in each radio block.
On the other hand, in the channel coding processing of GPRS, there are four kinds: type 1 to type 4. In the type 1, a burst error correction code having a bit length of 40 called fire code is adopted. In each of the type 2, type 3 and type 4, an error correction code of a different kind having a bit length of 16 is adopted. Depending upon the type, the type of transmitted and received communication data differs. Therefore, there is a problem that the type 2, type 3 and type 4 are affected by burst errors more easily than the type 1. By lengthening the burst length, occurrence of burst errors is reduced. However, the burst length of interleaving conducted in packet communication used in mobile communication such as portable telephone represented by GPRS is fixed to 4. Therefore, the burst errors cannot be reduced by lengthening the burst length.
As heretofore described, the burst length of interleaving conducted in packet communication used in mobile communication such as portable telephone represented by GPRS is fixed. This results in a problem that the burst errors cannot be reduced by adjusting the burst length.